Estimated depth of apatite and collagen degradation in human dentine by sequential exposure to sodium hypochlorite and EDTA: a quantitative FTIR study

AimTo characterize chemical degradation of the principal constituents of dentine after exposure to NaOCl and EDTA using Infrared Spectroscopy (ATR-FTIR). MethodologyGround dentine particles, from extracted permanent human molars, were passed through sieves of 38 to 1000m to provide six size ranges. Portions (250mg) of each size range were reacted with 5mL of 2.5% NaOCl for 2-10min; or 17% EDTA for 5-1440min. Powders larger than 75m were also sequentially exposed to NaOCl/EDTA/NaOCl each for 10min. All experiments were repeated five times. Reacted and unreacted powders were washed and dried. Particles larger than 75m were then reground. FTIR spectra of unground and reground reacted particles enabled assessment of particle surface versus bulk chemistry, respectively, plus estimation of reaction depth. Changes in the ratio of the 1640cm(-1) collagen: 1010cm(-1) phosphate peak height or its inverse were obtained. These were used to estimate surface and bulk fraction reacted and thus depth to which collagen or phosphate was reduced following immersion in NaOCl or EDTA, respectively. The data were analysed descriptively. ResultsSurface collagen fraction declined by similar to 40% within 2min of NaOCl exposure, and plateaued at similar to 60% between 6-10min. Bulk spectra showed average depth of collagen loss at 10min was 1613m. Ten minute EDTA exposure caused similar to 60% loss of surface phosphate. Average depth of phosphate loss was 19 +/- 12m and 89 +/- 43m after 10 and 1440min EDTA immersion, respectively. Sequential NaOCl/EDTA immersion yielded a 62 +/- 28m thick phosphate-depleted surface. Sequential NaOCl/EDTA/NaOCl treatment resulted in approximately 85m of collagen loss. ConclusionsData revealed the sequential depletion of collagen by NaOCl and apatite by EDTA in dentine, simultaneously exposing the other moieties. Alternate exposure to NaOCl and EDTA therefore enhances the depth of erosion.